The present invention relates generally to a method and apparatus for producing movement of an object on a fluid surface. More particularly, the present invention relates to inducing motion in a flexible object by exposure to a radiative or conductive energy source. Specifically, the present invention relates to using energy to alter the shape of a flexible object in contact with a fluid to produce a resultant displacement of the object from its original position.
In recent years, the introduction of smart materials have expanded the application of various materials. Smart materials are novel materials that respond to external stimuli such as a change in temperature, pH, moisture, or electric or magnetic fields. One example of such materials are piezoelectric materials, which change shape or some other property in response to the application of an electric field. One such material is disclosed by U.S. Pat. No. 5,350,966, which provides a piezocellular device that may be used as a propulsion device. The device converts electrical energy into fluid energy by causing the curvature of membranes with the application of an electric current.
One of the newest type of smart materials are liquid crystal elastomers. Liquid crystal elastomers are a new class of materials which combine a crosslinked network structure and the long range orientational ordering of the liquid crystal phase. The interaction between these two effects gives rise to materials with new phenomena which includes electrically and optically induced shapes changes, mechanically induced director reorientation, piezoelectric effects as well as additional effects. These materials combine the various broken symmetries of liquid crystalline phases with the elasticity of polymer networks.
One apparent property of these materials is that liquid crystal elastomers can readily undergo shape changes in response to external stimuli. Liquid crystalline elastomers have been described in U.S. Pat. No. 4,388,453, the disclosure of which is hereby incorporated by reference. The elastomers disclosed therein are organopolysiloxanes that have mesogenic pendant groups attached as side chains. The elastomers may be crosslinked by any of several means, including the use of organopolysiloxane crosslinking compound having at least two vinyl groups. Other polymers having liquid crystalline phases are described in U.S. Pat. Nos. 5,385,690; 5,190,689; 5,164,111; 5,151,481; 4,358,391; and 4,293,435; the disclosures of which are also incorporated herein by reference.
More recently, the shape changing response of nematic elastomers to light has been noted by Finkelman et al. (Physical Review Letters, 2 Jul. 2001, Vol 87, No. 1, pgs 015501-1–015501-4). Finkelmann et al. noted that, upon exposure to light, a nematic elastomer will reversibly change shape.